The present invention relates to a processing method using a probe of a scanning probe microscope and, more specifically, to a method of correcting drift of a processing position.
A microprocessing technology on the order of nanometer is required for improvement of level and degree of integration of functions, and research and development regarding processing technologies, such as local anodic oxidation or fine scratch processing using a scanning probe microscope (SPM), has been extensively carried out. Not only has microprocessing become important, but also processing with high degree of accuracy is now increasingly required.
In order to improve the accuracy of microprocessing, not only is the microprocessing capability or a highly accurate positioning technology important, but also reduction or correction of drift, such as thermal drift unavoidably generated during processing, have to be performed since processing using the SPM takes time. As a method of correcting drift on the order of 1 nm, a method of correcting a processing range in real time using a laser interferometer has been employed. The method using the laser interferometer has an advantage of real time, but since the amount of displacement of a mirror mounted to a stage is observed instead of the position near the processing point, there may be the case in which the amount of drift correction is different from that actually required. In particular, when the sample is a large sample such as a photomask or a wafer, the distance from the mirror and the actual processing point increases, and hence the tendency of being different from the actually required amount of drift correction increases correspondingly. When the temperature between the sample and the mirror is different, the laser interferometer cannot measure the thermal drift of the sample accurately, and hence the processing is performed after having waited until the sample and the mirror are thermally balanced.
In the processing using the SPM, the influence of the drift is reduced by performing the drift correction with the measured value of the laser interferometer or by repeating the process of observing the area including the processing point in an observation mode in the course of processing and then redefining the processing area before restarting the processing. In the method of observing in the observation mode and redefining the processing area before restarting the processing, if the processing area is large and observation is performed to an extent sufficient for the drift correction, it takes long time for observation, and hence there may arise a difference between the result of observation and the actually required amount of the drift correction, and in addition, the throughput is deteriorated. When the observation is made roughly, it does not take long time, but the accuracy of drift correction is disadvantageously deteriorated. Although a method of observing a characteristic pattern at the portion near the processing point in the course of processing and then performing the drift correction by pattern matching is also conceivable, there is a problem that there is no guarantee that a pattern which can be used for pattern matching both in X-direction and Y-direction always exists at the portion near the processing point.
In the case of defect correction of a photomask or manufacturing a sample for a transmission electron microscope using a focused ion beam, a method of processing including steps of opening small holes with a concentrated ion beam at positions near the processing point as drift markers, selectively scanning the area of several micrometers including small holes which are formed regularly by interrupting the processing in the course of the processing, obtaining the drift amount from displacement of the center of gravity of the small holes, and correcting the range of processing is employed, whereby the processing with high degree of accuracy of 20 nm or below is realized (for example, JP-B-5-4660 (P. 2, FIG. 11)). However, in the processing using the SPM, such a method has not been employed.
An atom-tracking method is developed as a method of tracking a substance of an atomic level size on the surface with atomic level accuracy. The atom-tracking method is a method developed for the scanning tunneling microscope (STM) which enables tracking of surface diffusion of an atomic size atom, in which a probe is rotated at a high speed substantially in radius of an atom in a horizontal plane, detecting a varied signal which depends on the position of a tunneling current by a lock-in amplifier, and giving feed-back to X-Y scanning (for example, B. S. Swartzentruber. Phys. Rev. Lett. 76 459-462(1996)), and has a potential for correcting the drift of 1 nm level in real time. However, it has not been used for the aforementioned drift correction.
The present invention is intended to enable processing with high degree of accuracy in a processing machine in which a scanning probe microscope is applied.